The present invention relates to a control method for a machine tool, which can drive a chiseling tool. A striker is accelerated directly by magnetic coils and strikes the tool. Machine tools of this type are known from the publication US 2010/0206593.
A machine tool has a tool receptacle, which is equipped to support a chiseling tool movably along an axis of movement. A magneto-pneumatic striking mechanism includes a primary drive, which is arranged around the axis of movement and has a first magnetic coil and a second magnetic coil in that order in the striking direction. The striking mechanism has a striker and a riveting head in that order in the striking direction on the axis of movement within the magnetic coil. Furthermore, the striking mechanism has a pneumatic spring acting on the striker in the striking direction. The respective inventive control method provides that during movement of the striker opposite the striking direction, a pressure sensor measures a prevailing pressure in the pneumatic spring. At the start of a drop in pressure in the pneumatic spring, a controller initiates an acceleration phase. The primary drive accelerates the striker in the striking direction during the acceleration phase.
The machine tool advantageously has a permanently and radially magnetized ring magnet between the first magnetic coil and the second magnetic coil along the striking direction comprised of a plurality of permanent magnets, for example. According to one embodiment of the control method, a first magnetic field generated within the first magnetic coil by the first magnetic coil is superimposed destructively on the magnetic field of the ring magnet during the acceleration phase and a second magnetic field generated within the second magnetic coil by the second magnetic coil is superimposed constructively on the magnetic field of the ring magnet during the acceleration phase.
One embodiment provides that in an active recovery phase, the striker is accelerated against the striking direction by means of the primary drive until the kinetic energy of the striker is sufficient to achieve the compression of the pneumatic spring that has been selected as a function of the striking energy of the striker. Until reaching the selected compression of the pneumatic spring, the active recovery phase is preferably followed by a resting phase, during which the primary drive is deactivated. Deactivation of the primary drive has proven advantageous to increase the efficiency of the striking mechanism. The efficiency of the primary drive drops with an increase in the compression of the pneumatic spring because the striker increasingly overlaps completely with the first magnetic coil. The duration of the resting phase is at least 10% of the duration of the active recovery phase, for example.
The inventive machine tool has a tool receptacle, which is equipped to support a chiseling tool movably along an axis of movement. A magneto-pneumatic striking mechanism has a primary drive, which is arranged around the axis of movement and has a first magnetic coil, a permanently and radially magnetized ring magnet, for example, comprised of permanent magnets, and a second magnetic coil, following one another in that order in the striking direction. The striking mechanism has a striker and a riveting head in that order in the striking direction on the axis of movement within the magnetic coils. Furthermore, the striking mechanism has a pneumatic spring, which acts on the striker in the striking direction. The pneumatic spring may be arranged partially or completely inside the first magnetic coil. A pressure sensor is provided for determining the pressure in the pneumatic spring. A controller may carry out the control method according to the invention or an embodiment thereof.